My 1995 yj shakes and vibrates the entire vehicle when i maintain a speed around 25-30 mph right before it shifts into 3rd (automatic Tranny). could this be something wrong with the tranny or transfer case or driveshaft?

could be as simple as U-joints. Mine vibed real bad through 3rd gear until i changed the U-joints in my rear drive shaft. It's pretty smooth now. If you've changed the ride height or angle of the shaft at all recently i'd look at them first.